The present invention relates to an electronic system for a battery comprising a least one sealed storage cell.
An electrochemical cell or storage cell (these two terms being equivalent, the term storage cell will be used hereinafter) is a device for producing electricity in which chemical energy is converted into electrical energy. The chemical energy is constituted by electrochemically active compounds deposited on at least one face of electrodes arranged in the storage cell. The electrical energy is produced by electrochemical reactions during discharge of the storage cell. The electrodes, arranged in a container, are electrically connected to current output terminals to provide electrical continuity between the electrodes and an electrical consumer with which the storage cell is associated.
The battery is designed to supply electrical energy to an external application; a charging circuit is consequently generally provided to which the battery can be connected in order to recharge the cells. To increase output power, it is known to associate several sealed cells in order to form a battery. The battery then comprises one or several parallel branches of cells connected in series. Battery charge and discharge management can then be arranged and controlled in order to balance charging and discharge of the various cells one with respect to the others. A control circuit, which may be more or less complex depending on the application, is generally provided to be associated with the battery.
In those applications employing a battery for standby power, it is essential for the cells to be charged to their full capacity prior to use, but, above all, for power to be instantaneously available.
Aircraft or other transport vehicles generally employ lead acid or nickel cadmium type (NiCd) batteries for starting the vehicle and for standby power. Such batteries can remain connected to the main power supply and be charged while demands are not being made on them; there is no fear of overcharging the cells. Now, it has appeared desirable to be able to employ lithium ion (Li-ion) type batteries as a standby battery, notably for application to aircraft in order to be able to benefit from the reduction in weight and ease of maintenance inherent to this type of battery. However, lithium ion type batteries require specific charging management in order to avoid any overcharging. It has indeed been observed that overcharging lithium ion storage cells leads to premature ageing of the battery. It is consequently not possible to directly replace a NiCd or lead acid battery by a lithium ion battery; an electronic battery management system needs to be provided for controlling charging and balancing of lithium ion cells.
Further, it is desirable for a standby battery to be able to deliver electrical energy to the application for which it is designed in a fast, reliable fashion without discontinuity when the main power supply of the application is subject to failure.
There is consequently a need for a battery which can be on charge permanently without the risk of overcharging while no demands are being made on it by the external application and which can supply electrical energy without discontinuity when demands are made on it.